This invention relates to a means and method for increasing compression strength of corrugated cardboard boxes.
In the past, compression strength of corrugated boxes has been determined primarily by the weight of the linerboards used in their manufacture. Appropriate combinations of the liner weights of the three layers of corrugated board may be used to achieve a desired compression strength. In general, the heavier the combined board weights, the higher is the compression strength of the box.
More recently, efforts have been made to increase the compression strength of boxes by using linerboard manufactured by various methods which result in the use of less or equivalent fiber, while providing increased compressive strength. There are several methods currently employed. One method makes use of board which is manufactured using specialized machinery which allows the paper fibers to orient themselves predominantly in the machine direction. This method produces board of increased strength by utilizing the strength intrinsic to the fiber's directional mode. To effect this result, specialized machinery and manufacturing processes are required. Another method employed, which also requires specialized machinery, is to press the board such as to increase the density, while reducing the finished board moisture content resulting also in greater compressive strength. These methods can result in compression strength increases in the order of 10-20%.
Other methods rely on chemical impregnation or saturation of the sheet with resins or inorganic salts which form paper/chemical composites which have greater stiffness and compressive strength. Using such methods the entire linerboard is subjected to chemical treatment. Problems resulting from these methods include difficulty in being able to glue the board in box manufacturing operations, as well as cracking of the score lines resulting from the increased stiffness. In the case of saturation with salt solutions, the only successful methods have relied on use of saturating equipment usually beyond the economic constraints of most box manufacturers.